Webinar Vet April 27, 2017 Feline Hyperthyroidism: …...Webinar Vet April 27, 2017 Feline Hyperthyroidism: talking points Andrew L Bodey BVSc CertVR MRCVS Learning Objectives Background

© The Hyperthyroid Cat Centre, April 27, 2017 Page 1 of 13

Webinar Vet April 27, 2017 Feline Hyperthyroidism: talking points

Andrew L Bodey BVSc CertVR MRCVS

Learning Objectives

Background

The diagnosis – blood testing Which

tests? Are in-house test results concordant with external reference results? How

reliable and repeatable are external reference laboratories?

Management of FH Methimazole

Radio-iodine

homeopathy

Evidence-based medicine

Selected references

Multiple Choice Questions

Learning Objectives

• Understand some of the limitions of laboratory data in diagnosing feline hyperthyroidism

• An improved awareness of potential adverse effects of methimazole

• An awareness of published claims of homeopathy in treating feline hyperthyroidism and the results of a prospective placebo-controlled randomised clinical trial using homeopathy

• An improved understanding of evidence-based medicine and its relevance to clinical practice.

Background Since 1979, feline hyperthyroidism (FH) has a continually rising prevalence, up to 20% of cats above 10 years of age in 2013. Hyperthyroidism is underdiagnosed; perhaps 10% of well cats over 10 years of

age.

It is the commonest endocrinopathy in older cats but is better thought of as the commonest neoplasm in older cats. Prevalance of carcinoma rises from 3% to 20% after 4 years of methimazole

Aetiology most likely multifactorial Common clinical signs include:

• Weight loss

• polyphagia

• tachycardia

• goitre

• polydipsia & polyuria

• D+ & V+

• secondary hepatopathy

• secondary LV hypertrophy

• behavioural changes

http://www.youtube.com/watch?v=IoZo43bO_5o





The diagnosis – blood testing – which tests? Key points:

1. Total T4 is the test of choice to confirm a clinical diagnosis of FH.

2. Free T4 can support a diagnosis of FH when total T4 is in the high-normal range BUT

a. ~16 % of euthyroid cats have elevations in free T4

b. Non-thyroidal illness can depress total T4 into the euthyroid range.

3. TSH is currently not validated in cats but can support a diagnosis of FH when the result is

suppressed below detection as is seen in virtually 100% of FH cases. Finding detectable TSH should lead to the diagnosis of FH being questioned.

4. Equivocal total T4 results (eg in high-euthyroid range) can be checked by

a. Repeating the same test using the same machine after a suitable delay, such as

6-8 weeks

b. Repeat total T4 on the current sample using a different machine

c. Add free T4 to the current test panel

d. Check clinical signs are compatible, such as presence of a goitre

e. Bear in mind that all test methods, whether in-house or exernal reference

laboratories, are approximations

f. Consider scintigraphy, if available.

5. Concordance of in-house and reference laboratory results may or may not be high –

results may differ not only numerically but also in category (see below for an example).

6. Reference laboratories report results to the nearest 0.1 nmol/l implying a high degree of accuracy and precision. This assumption is not justified – see the example results

below.

Are in-house test results concordant with external reference

results? Using IDEXX Catalyst as an example (other manufacturers should be able to provide equivalent data):


These are the validation data produced by IDEXX comparing the in-house Catalyst (in rows) with the reference laboratory Microgenics (in columns). Talking points are:

Microgenics

low normal high totals

Catalyst low 4 2 0 6

Normal 7 128 3 138

high 0 7 69 76

Totals 11 137 72 220

Of 137 euthyroid cats, Catalyst recorded 2 as low = 1.5%

7 as high =5.1%

Of 138 cats that Catalyst recorded as euthyroid, 7 were low = 5%

3 were high = 2.2%

Microgenics



Normal 7 128 3 138


high 0 7 69 76

Totals 11 137 72 220

Of 72 hyperthyroid cats, Catalyst recorded 3 as normal = 4%

Of 76 cats that Catalyst recorded as hyperthyroid, 7 were normal = 9.2%

Microgenics



Normal 7 128 3 138

high 0 7 69 76

Totals 11 137 72 220

Of 11 hypothyroid cats, Catalyst recorded 7 as normal = 63.6%

Of 6 cats that Catalyst recorded as hypothyroid, 2 were normal = 33.3%

Potential clinical implications may be:

Of 137 euthyroid cats, Catalyst recorded 2 as low = 1.5% Supplemented?

7 as high = 5.1% Over-treated?

Of 138 cats that Catalyst recorded as euthyroid, 7 were low = 5% Not supplemented?

3 were high = 2.2% No treatment?

Of 72 hyperthyroid cats, Catalyst recorded 3 as normal = 4% No treatment?

Of 76 cats that Catalyst recorded as hyperthyroid, 7 were normal = 9.2% Over -treated?

Of 11 low cats, Catalyst recorded 7 as normal = 63.6% Not supplemented? Of 6 cats that Catalyst recorded as low, 2 were normal = 33.3% Supplemented?

Key considerations with these data are:

1. The validation data is collected by running the same sample on the respective machines.

2. This validation table CANNOT describe a predictive value (positive or negative) for either test as

there is no attempt to describe the test population from which the samples were collected. This is critically important:

a. If your protocol tests all cats over 8 years of age, for example, cats at the younger end of

the range are much less likely to have FH and false positive results are more likely.

b. If your protocol only tests older cats with a clinical diagnosis of FH, false negative results

are more likely.

A current published paper draws the following conclusions (Peterson 2017):

1. No statistical difference between Catalyst or Microgenics for total T4

2. Excellent correlation with mean difference of 2.5 nmol/l

3. No fixed or proportionate bias


4. Of 150 samples, 95.5% agreement for category (hypo-, eu- or hyperthyroid)

5. “Catalyst provides accurate and reliable total T4 results over a wide, clinically useful range in cats, providing in-clinic results equivalent to those obtained by a reference laboratory”. Which begs the question:

How reliable and repeatable are external reference laboratories?

See the European Society of Veterinary Endocrinology Quality Assurance Scheme.

They send standardised samples and submit them to all participating laboratories and produce the

following example results. Each participating laboratory tests the same sample. Blocks in the same colour indicate the same methodology was used. The key point is that even amongst reference

laboratories using the same machine, results vary substantially. Reporting results to the nearest 0.1 nmol/l implies precision and accuracy – these results illustrate that this degree of confidence in results

is unfounded. In these examples the repeatability of results across all test methods is shown by %

coefficient of variation, defined as (𝑚𝑒𝑎𝑛 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛⁄𝑚𝑒𝑎𝑛 𝑝𝑎𝑟𝑎𝑚𝑒𝑡𝑒𝑟)𝑥 100. For example, a mean parameter of 100 units with a standard deviation of 10 units would have a

coefficient of variation of 10%.

Total T4 % coefficient of variation across all methods using 33 laboratories: 19.5%


Free T4 % coefficient of variation across all methods using 12 laboratories: 27.4%

TSH % coefficient of variation across all methods using 24 laboratories: 35%.


Key considerations with these data are:

1. The Quality Assurance Scheme is affected by the participants. Some test methods are used

more commonly than others and it does not follow that the outlying results are more or less

likely to be right or wrong than more commonly reported results.

2. Technology that relies on careful technician involvement has a substantial opportunity for error especially if sample dilution is required.

3. Reference results for total T4 reported to the nearest 0.1 nmol/l imply a high degree of accuracy

and precision which is not in fact the case. Even using the same test method, the variation in

results is much greater than +/- 0.1 nmol/l – for a result of say 40 nmol/l the variation is more

likely to be in the region of +/- 8 nmol/l.

4. Different test methods produce substantially different results THEREFORE it is invaluable to

follow the same patient using the same test method throughout the period of diagnosis,

treatment and monitoring. Switching between different test methods makes comparison of

results unreliable and potentially misleading leading to inappropriate clinical decisions.

Key points for the future: 1. Look out for upcoming research into current test methods

2. Look out for new test technology such as liquid chromatography mass spectrometry

Management of FH Medication In the following licensed and unlicensed preparations, the active ingredient in all cases is

methimazole: Felimazole (Dechra, methimazole) and then as

Vidalta (MSD, carbimazole), a slow-release tablet

Thiafeline (Animalcare, thiamazole), in blister packs

Thyronorm (Norbrook, thamazole), oral liquid preparation Off-license transdermal methimazole gel

Most cases respond within 2-3 weeks of initiating medication

• Is reversible

• Can be used as preparation for curative treatment, or be continued life-long

• Requires client compliance

• Requires cat compliance

• Requires an absence of adverse effects

• Potentially teratogenic in people – wear gloves with cat litter tray


• Not recommended to crush tablets

Methimazole

1. Oral medication side effects are reported as:

• Of 262 cats, typically within the first 1-2 months of starting medication, adverse effects can

occur (Peterson1988)

• in 18.1% of cats: – Anorexia

– Vomiting

– Lethargy

– Excoriation of face and neck

– Bleeding

– Jaundice secondary to Hepatopathy

• In 16.4% of cats:

– eosinophilia

– Lympocytosis – Slight leukopenia


– Agranulocytosis

– Thrombocytopenia

– Immunological reactions include


– Antinuclear antibiodies (significance uncertain)


– Red cell autoantibodies

Adverse effects reported more recently:

– Generalised lymphadenomegaly (Atkinson, 2008)

– Vasculitis with digital and tail necrosis, and renal infarcts (Bowlt 2013)

NOTE: methimazole can induce a hepatopathy; consider stopping medication if liver parameters increase.

Side effects most often seen within 1-2 months of starting –

Important to be vigilant after a dose increase

– Usually reversible if detected and drug withdrawn

– Requires sufficient checks to detect more subtle changes

– Consider prompt blood sampling in an unwell or anaemic cat currently taking methimazole.

– Manufacturer recommends 3, 6, 10, 20, then every 12 weeks after starting

2. Oral Medication Side effects reported by UK general practitioners (Higgs, 2014) Side effects observed in the 12 months prior to a survey of 603 vets:

- 69% vomiting


- 47% anorexia

- 44.8% facial pruritus

- 22.7% azotaemia

- 11.8% anaemia

- 10.9% leukopenia

- 9.6% hepatic damage

- 8.4% neutropenia

- 8.4% thrombocytopenia

- 4.7% lymphadenopathy

- 0.9% sudden death

-

How representative are these reports?

Of UK vets observing side effects, the following reported them to the VMD adverse

event surveillance scheme:

- 49.6% of vets reported none of the adverse effects they had observed

- 36.5% reported up to 25% of adverse effects - 8% reported 26 – 99% - 5.9% reported

100%.

If methimazole adverse effects are suspected – what next?

1. Remember to report all suspected adverse events to the VMD.

2. Consider the following actions for the clinical case according to the list

on the left:

a. Green: re-introduce at lower dose / try alternative formulation

& monitor

b. Red: discontinue permanently (adverse events in bold – may

become life-threatening)

c. Black: reconsider routine treatment choice in future cases?

3. Online survey of owner experience with oral medication (Caney 2013) •

Client-perceived outcome as “helped a lot” or “cured”:

– Felimazole group 75% (28 cats)

– Vidalta group 72.2% (18 cats)

• Client medicating reliability (111 clients)

– No problem medicating – 51.4%

– Monthly struggles – 16.2%

– Weekly struggles – 19.8%


– Daily struggles – 12.6%

• Overall, reliability of medication at least 75%

• Overall, unreliability of medication up to 25%

– Best results with pill pockets

– Worst results with tablet crushing

Radioiodine

1. Treatment outcomes: Radioiodine treatment of 524 cats (Peterson 1995)

• In 85% of cases T4 returns to normal range within weeks (mean 9.5 days)

• 15.3% are delayed responders remaining hyperthyroid but cured by 6 months

• Approximately 2.5% show recurrence in the future (mean 3 years)

• 1.5% remain hyperthyroid at 6 months

– most of these respond to a second treatment

– suspect carcinoma if still unresponsive

• radioiodine treatment of choice for carcinoma, but at high dose

• 2.1% required supplementation with thyroxine, if

– clinical hypothyroidism (excessive weight gain, perhaps hair loss, often personality

changes – become subdued/withdrawn)

– concurrent azotemia (Williams 2010) nb: life expectancy reduced by half if this group are not diagnosed and treated.

Summary: 94.2% cure rate, occasional thyroxine supplementation required, occasional

nonresponders, double the life expectancy of cats on longterm methimazole.

2. Client-perceived outcome (Caney, 2013) Perceive

as “cured”:

– 94.1% (of 17 cats) Perceived as “helped alot”:

– 5.9%

Perhaps this may reflect more stable thyroxine control;

“Inconsistent T4 concentrations with extremely high variations between the testing intervals

could be a possible explanation for the observed shorter survival time [of cats on methinazole] compared with radioiodine treated cats” (Boretti 2013)


Homeopathy – why investigate this modality? Conventional treatments have limitations

Methimazole is not a benign drug

Iodine-restricted diet is unpalatable in most cases and a clinical response is not always seen

radio-iodine is still of limited availability – though in the UK this is changing Surgery carries risks of morbidity and mortality Reported efficacy:

Oral methimazole 87.4%

Iodine-restricted diet 23 - 90% (after 8 and 12 weeks respectively)

Thyroidectomy 78 - 95%

Radio-iodine 94.2%

Homeopathy 66.7 - 75% show moderate or major improvement in clinical signs

75% in one case series reported a successful clinical response

Recent trial published under the title: Double-blinded randomised placebo-controlled clinical

trial of individualised homeopathic treatment of hyperthyroid cats.

Inclusion criteria: Total T4 > 66 - < 160 nmol/l

Exclusion criteria: Significant concomitant non-thyroidal illness

Visit 1

Baseline data: Body weight, heart rate, haematology, biochemistry, clinical assessment

Recruited cases were assigned to placebo or homeopathy,

Blinded by preparation of 2 batches of identical dropper bottles with sequential numbering and

8mls purified water + 2mls 40% ethanol

1st batch remained with homeopath

2nd batch kept by a key holder at a separate address.

Individualised homeopathic medicine prepared using the 1st batch of bottles

Homeopathic assessment relied upon a “constitutional questionnaire” and computer programme The sarcode throidinum and the most appropriate individualised simillimum potentised by a process of succession to a potency of 30c.

Each subject randomly assigned to placebo or homeopathy using a computer-generated

random list and the appropriate bottle dispensed to the cat owner

1 - 3 drops were applied to the gums by the owner for 21 days

Visit 2

Interval of 21 days after Visit 1

Repeated the same data as collected at Visit 1 ie body weight, heart rate, haematology,

biochemistry, clinical assessment

Those cases that were euthyroid were able to leave the trial and continue under the care of the homeopath.


Those still in the defined hyperthyroid range were prescribed methimazole (Felimazole 2.5 mg

bid) for 21 days

Visit 3

Interval of 21 days after Visit 2

Repeated the same data as collected at Visit 1 & 2 ie body weight, heart rate, haematology, biochemistry, clinical assessment Data collection completed.

Statistical analysis by blinded statistician.

Statistical significance defined as P< 0.05.

Of 40 recruited cases:

Placebo 19 Homeopathy

21

Results Between visits 1 & 2, comparing the placebo and homeopathy groups:

Changes in total T4 P value 0.96

Changes in heart rate P value 0.36

Changes in body weight P value 0.16

At Visit 2, two cases failed to meet the inclusion criteria:

Case 11: total T4 reduced from 71.6 to 60 nmol/l.

– Outcome: encountered diabetes mellitus and renal insufficiency and euthanased Case

35: total T4 reduced from 66.3 to 40.7 nmol/l.

– Outcome: encountered multicentric lymphoma and euthanased.

Results Between visits 2 & 3, comparing all cats:

Changes in total T4 P value <0.0001

Changes in heart rate P value <0.0001

Changes in body weight P value <0.0001

No difference between placebo and homeopathic groups

Evidence-Based Medicine - Key Points

1. Keep an open mind. It is best to approach all information/evidence sources trying to identify

truth – that which is in accordance with the facts.

2. Be aware of limitations of study design. How accurate and precise are the test methods

relied upon?

3. Look for bias in the information/evidence source you are relying on. What are the

presumptions of the source?

4. Look for bias in your own interpretation of the information/evidence source. What are your

own presumptions? In this example, perhaps that homeopathy couldn’t be efficacious, or

that homeopathy couldn’t be investigated by this study design?

As an example, what of the case series claiming 75% efficacy for homeopathy? Four

cases were recruited (Chapman 2011):


Given the previous discussion on

testing total T4 and free T4 and the

prevalance of elevated free T4 in

normal euthyroid cats, were the authors able to assert a diagnosis of

hyperthyroidism in all cases in the

series?

Selected References

• Milner RJ, Channell CD, Levy JK, Schaer M. Survival times for cats with hyperthyroidism treated with iodine 131, methimazole, or both: 167 cases (1996 – 2003). JAVMA 2006: 228: 559 – 563

• Gallagher B, Mooney CT. Prevalence and risk factors for hyperthyroidism in Irish cats from the

greater Dublin area. J Vet Intern Med 2013;27:689.

• Peterson ME, Kintzer PP, Hurvitz AI. Methimazole treatment of 262 cats with hyperthyroidism. JVetIntMed 1988 2: 150-157.

• Peterson ME, Becker DV. Radioiodine treatment of 524 cats with hyperthyroidism. JAVMA 1995

207: 1422 – 8.

• Bowlt K, Cattin I, Steward J. Carbimazole-associated hypersensitivity vasculitis in a cat. JSAP 2013 Nov

• Williams TL, Elliott J, Syme HM. Association of iatrogenic hypothyroidism with azotemia and

reduced survival time in cats treated for hyperthyroidism. JVIM 2010 24: 1086-92

• Chapman SE. Homeopathic and integrative treatment for feline hyperthyroidism – four cases.

Homeopathy 2011 100: 270 – 274

• Atkinson, M. Lymphadenomegaly associated with carbimazole. JSAP 2008 49: 426

• Boretti FS et al. Transdermal application of methimazole in hyperthyroid cats: a long-term follow-up study. JFM&S 2013: epub

• Higgs, P, Murray, JK, Hibbert, A. Medical management and monitoring of the hyperthyroid cat:

a survey of UK general practitioners. JFM&S. (2014). Online publication.

• Caney, S.M.A. An online survey to determine owner experiences and opinions on the

management of their hyperthyroid cats using oral anti-thyroid medications. JFM&S. (2013). 15:

494-502.

• ME Peterson, M Rishniw, GE Bilbrough (2017). Validation of an in-clinic point-of-care

immunoassay for measurement of total T4 concentration in serum from euthyroid and

hyperthyroid cats. JVIM 31: 254-255

• Bodey, AL., Almond, CJ., Holmes, MA.(2017) Double-blinded randomised placebo-controlled

clinical trial of individualised homeopathic treatment of hyperthyroid cats. Veterinary Record

180, 377

Case T4 Free T4 Response?

1 81.1 - X

2 38.4 58 √

3 42.5 72 √

4 38.4 59 √

Normal range <32 nmol/l <51 pmol/l

Documents

Webinar Vet April 27, 2017 Feline Hyperthyroidism: …...Webinar Vet April 27, 2017 Feline Hyperthyroidism: talking points Andrew L Bodey BVSc CertVR MRCVS Learning Objectives Background